The present invention relates generally to holding mechanisms and more particularly to a spacecraft having a mechanical holding mechanism which is substantially free of microdynamic noise.
Movable structures such as solar arrays, antennas, masts, sensors, and the like, are frequently used in spacecraft applications where large structures are required when the spacecraft is in orbit but a compact structure is required when launching the spacecraft. The movable structures are typically stowed during launch and are subsequently deployed at a preselected time after the spacecraft decouples from the launch vehicle. After deployment, the movable structures are each positioned to a preselected location by a positioning mechanism such as an actuator or a spring.
A separate mechanical latching mechanism, such as a mechanical clamp, is typically used to hold the movable structures in the preselected locations. Mechanical latching mechanisms typically have at least two mechanical surfaces which are in physical contact with each other, examples of which are the pin and jaws of a mechanical clamp. When these two mechanical surfaces move with respect to each other, microdynamic noise is generated, which in turn generates low levels of vibration in the movable structure. This microdynamic noise is generally at a micro-G level and is therefore not a concern for most spacecraft applications. However, for spacecraft applications which require an ultra-quiet dynamic environment, such as a spacecraft having a spaced-based interferometer, microdynamic noise can interfere with the mission of the spacecraft and can perturbate the data gathered by the spacecraft.
Methods have been suggested to combat microdynamic noise. One such method consists of isolating and highly damping the source of the microdynamic noise. However, this is difficult to accomplish in practice. Another method consists of removing moving parts, such as hinges, from the load path once the movable structure is positioned to the preselected location. This is also difficult to accomplish in practice. Yet another method applies large amounts of preload to the holding mechanism, such as latches, in attempts to prevent slippage which generates microdynamic noise. However, evidence exists that sufficient preloads cannot be applied to bearings or latches to remove all microdynamic noises. Lastly, a technique of maintaining the structures at a constant temperature within a narrow band of temperatures has been suggested so that the structures do not expand and contract and generate microdynamic noise. This is very difficult to accomplish in practice and requires precision heating or cooling of the structure which is expensive, requires additional equipment on the spacecraft and extracts a large weight penalty.
What is needed therefore is a method to reduce the microdynamic noise in a high precision spacecraft which has a movable structure in which the method is relatively simple to accomplish in practice and does not exact a large weight penalty.